Heat treatable beta titanium base alloy and processing thereof

ABSTRACT

A TITANIUM BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT 7 TO 9% EACH OF MOLYBDENUM AND VANADIUM, 1.5-2.75% IRON, 2.5 TO 3.5% ALUMINUM AND THE BALANCE TITANIUM.

HEAT TREATABLE BETA TITANIUM BASE ALLOY AND PROCESSING THEREOF FiledMarch 16, 3.966

lo @om manor xmc' wzq OhrJ ON ISd OOOlX-HLNiLS CIIBI .LISddO 'ZZO:NvaNTOR- B. HUNTEQ Harem' w. reosemaaaq DONQLD QTTOQNEVS United StatesPatent O 3,595,645 HEAT TREATABLE BETA TITANIUM BASE ALLOY AND PRCESSINGTHEREOF Donald B. Hunter and Harry W. Rosenberg, Henderson,

Nev., assignors to Titanium Metals Corporation of America, New York,N.Y.

Filed Mar. 16, 1966, Ser. No. 534,759 Int. Cl. C22c 1 5/ 00 ABSTRACT OFTHE DISCLOSURE A titanium base alloy consisting essentially of about 7to 9% each of molybdenum and vanadium, 1.5-2.75% iron, 2.5 to 3.5%aluminum and the balance titanium.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes Without the payment of anyroyalty thereon.

This invention pertains to heat-treatable, beta titaniumbase alloys, andmore particularly to a novel alloy of this type of critically-limitedalloy content such as to impart a combination of useful propertiesrendering the same superior in Various respects to previously knowntitaniumbase alloys of the substantially all-beta type.

The alloy of the invention consists essentially as to composition ofabout 7 to 9% each of molybdenum and vanadium, 1.5 to 2.75% of iron, 2.5to 3.5% aluminum, and the balance titanium except for interstitials andimpurities within commercial tolerances. The preferred cornposition ofthe alloy for most commercial applications is about 8% each ofmolybdenum and vanadium, 2% iron and 3% aluminum, balance substantiallyall titanium.

As missions become more sophisticated, and as aerospace vehicles becomelarger, the more important structural efficiency becomes. Structuralefciency entails not only high ratios of strength to weight but alsoresistance to all forms of cracking. Moreover, in order that a designercan take maximum advantage of an alloys tensile properties, theseproperties must be attainable throughout sections of varying thicknessunder a wide variety of service conditions. Notched fatigue strength,crack initiation and propagation resistance and metallurgical stabilityare particularly important. The alloy of this invention represents animprovement in the present state of the art in these respects.

Also from the producers and fabricators points of view, formability andaging response are important aspects in component manufacture. The alloyof this invention as solution treated above the beta transus has arelatively low yield strength on the order of 120,000 p.s.i., 0.2%offset and excellent ductility on the order of 16% elongation in 2" forease of forming. As thereafter aged at about 900 F. for a relativelyshort time of about 24 hours, the ultimate and yield strengths areincreased to about 200,000 and 190,000 p.s.i., respectively, withretention of good ductility of 5% or better in tensile elongation. Aunique property of the aged strength of the alloy is that it remainssubstantially constant at the above level on further prolonged agingtreatment, and in this respect dilers remarkably from the commercialTil3Vl1Cr3Al alloy, the aged strength of which progressivey increaseswith time of aging treatment and never attains the relatively constantplateau strength of the instant alloy. Also the aged yield strength ofthe instant alloy increases much more rapidly with aging time than thatof the commercial alloy. Thus the aged ultimate strength of the instantalloy attains a value of 180,000 p.s.i. in 8 hours as against only about138,000 p.s.i.. of the commercial alloy within that aging period. Alsoas developed below the alloy of this invention is superior in variousother respects to the Ti-l3V-llCr-3A beta alloy, which heretofore hasbeen the best commercial alloy of this type.

The alloy of the present invention may be produced as flat rolled millproduct or in such other forms as forgings, extrusions or wire byconventional fabrication techniques. The room temperature and 600 F.tensile properties of the preferred Ti-8Mo-8V-2Fe-3Al modification areshown in the following Tables l and II:

TABLE L-ROOM TEMPERATURE TENSILE PROPERTIES OF Ti-8 Mo-S V-2 Fe-3 Al.AGED AT 900 F.

[0.060" thick sheet, solution treated 1,500" F.-10 minutes-Water 1Sample aged after machining and tested with oxidized surface.

TABLE IL600 F. TENSILE PROPERTIES [0.060 thick sheet solution treated asabove] Elongation percent in 2" Aging heat UTS YS Unitreatment K s.i. Ks.i. Local form Total Modulus 8 hours-AQ..- 167 142 10 1 4 14. 6 24l1ours-AC 170 154 22. 5 1. 25 3. 5 14. 0

From the data of Table I it will be seen that the alloy of thisinvention when recrystallized by aging from the solution-treatedconditions attains a yield strength of 180,000 p.s.i., i.e. 180K s.i.after aging for 8 hours at 900 F., and therea'fter prolonging the agingtime to 64 hours results in only a small further strength increase up toabout K s i. attained in 24 hours.

This is also shown graphically in the accompanying drawing which alsoshows the aging response f-or the commercial Ti-13V-l1Cr-3Al alloy. Notethat after aging for 8 hours at 900 F., Ti-SMo-SV-2Fe-3Al reaches a,plateau of high strength in the range of 180-190K s.., whereas thecommercial alloy Ti-l3V-11Cr-3Al possesses a yield strength of only 140Ks.i. and continues to gain strength with increasing Aaging time, so thatno plateau of constant strength is attained within 32 hours. Thistherefore is an important advantage of Ti-8Mo-8V-2Fe-3Al over Til3V-11Cr-3Al, that it ages rapidly to a 180K s.i. yield strength, andthereafter undergoes little change in strength. This lack of a criticaltime for aging the Ti-8Mo-8V-2Fe-3Al alloy thus constitutes an importantaspect of this invention. Furthermore, whereas the Ti-13V-llCr-3Al alloyis very difiicult to age to a preselected strength level, the agedstrength of Ti-SMo-8V-2Fe-3Al alloy can be readily controlled byselection of proper aging temperature. Higher aging temperatures resultin lower strength and vice versa.

Moreover, as shown by the test data of Table II above, the alloy of thisinvention retains a useful degree of strength up to 600 F. That is tosay, in the aged condition the alloy typically retains up to 600 F., 80%0f its room temperature strength.

The notched fatigue properties of the alloy of this invention are shownbelow in Table III, from which it will be evident that the notchedfatigue run out strength of the Ti-8Mo8V2Fe3Al alloy lies in the rangeof 30-35K s.i.

By contrast the notched fatigue limit of the commercial 10Ti-l3V-l1Cr-3Al alloy is only 20-25K s.i. at run out time of 10'1cycles. This superiority in notch fatigue is another important featureof this invention.

TABLE III Room temperature notched fatigue properties 1 (Specimen heattreated 1450 F.-10 min- AC +900 F.-8 hrs-AC) 1 Sheet specimens tested ata minimum to maximum load 3 ratio (R) of 0.25 at a notch concentrationfactor of K:3.5.

TABLE IV.-SUMMARY OF PROPERTIES OF Ti8 M08 V-2 Fe 3 Al ALLOY (0.060SHEET) v Property Value Density, lb./cu. inch 0. 175 Aunealed yieldStrength, K s. 118-120 Annealed strength/weight ratio, in.- 680, 000Aged yield strength:

900 F.-8 hours age (strength weight ratio) K s.i. l 180 900 F.-16 hoursage (strength/Weight ratio) K s.i 2 186 900 F.-24 hours age(strength/weight ratio) K s.i... 3 191 Room temperature notch tensile:

900 F.8 hours age, K s.i.- 172 NTS/UTS ratio 4 0.87 900 F.-24 hours age,K s i. 164 NTS/UTS ratio 0. 83 -65 F. Notch tensile (900 F.8 hours AC) Ks.1 145 600 F. notch tensile:

900 F.-8 hours age, K s.i. 184 NTS/UTS ratio 1.10 900 F.-24 hours age Ks 188 NTS/UTS ratio 1. Kre value; 900 F.8 hours age, 45,000 Notchedfatigue strength, 900 F.-8 hours age, K s 5 30-35 Minimum bend radius;1,500 F.-10 minutes-AO 2T 1 7% elongation (1,030,000 in.1).

2 7% elongation (1,060,000 in.1).

3 5% elongation (1,090,000 in.1).

4 Notched tensile strength/ultimate strength ratio. Stress for 10million cycles.

A further feature of this invention is that Ti-8Mo-8V- 2Fe3Al alloydisplays a superior resistance to stress corrosion cracking at 800 F.induced by the presence of salt, Table V below, than the commercial betaalloy Ti-13V-11Cr-3Al. In view of the growing importance of the relativesusceptibility of titanium alloys to stress corrosion, this alsoconstitutes an important advantage of this invention over the presentstate of the art.

TABLE V.COMPARISON OF HOT SALT STRESS CORROSION BEHAVIOR OF T1-8 M0-8 V2Fe-3 Al .AND Ti-l3 V11 Cr-3 Al ALLOYS (BOTH IN SOLUTION TREATED AND AGEDCONDITIONS) Bend Result of Alloy radius Treatment attening 'Tl-8 Mo-BV-2 Fe-B Al 6T None (control) No cracks. Seme as above 6T 800 F.-2hours, no salt Do. Do- 5. 6T 800 F.-2 hours, salt coated,..- Do. Do--.5.71 do Do. Do 6T -....do Do. 'Pl-13 V-11 (Jr-3 A1-.. 5. 8T None(control) Do. Same as above 5. 8T 800 F.-2 hours, no salt Do.

o 5. 8T 800 F.-2 hours, salt coated Numerous small cracks. Do 5.8'1 doDo. Do... 5.8'1 do Do.

The following Table IV gives a summary of the mechanical properties ofTi-8Mo8V2Fe-3Al. From this it is seen that this alloy possesses goodnotch toughness, even in the fully aged condition, (900 F.-24 hours),and

also retains good notch toughness over a range of temperatures from F.to 600 F. This notch toughness is an important feature of thisinvention.

From the above data it will be seen that whereas the alloy -of theinstant invention is immune to salt corrosion cracking under theconditions o'f testing, the Ti-l3V- 11Cr-3Al alloy of the prior art wasnot.

A further useful property of Ti-8'Mo-8V2'Fe-3Al alloy of this inventionis that even after exposure to temperatures of 600 F. for 500 hoursunder load it sill retains a useful amount of ductility 'as shown in thefollowing Table VI. Ductility is also found when samples of this alloyare tested after exposure to aging temperature without subsequentpickling to remove the oxidized surface, Table I.

TABLE VI.CREEP STABILITY DATA ON Tl-8 Mo-S V-2 Fe3 Al ALLOY ExposureElon- Percent gation Tempera- Stress, Time, defor- UTS, YS, percentModulus ture, F. K s.i. hours mation K s.i. K s.i. in 1" p.s.i. X100 lHeat treatment prior to exposure -1,500 F. for 10 minutes and waterquenched followed by aging at 900 F. for 8 hours and air cooled. 1 Sameas above except for aging424 hours.

From the standpoint of practical useage it is important that titaniumalloys be Weldable. Data in Table VII below, shows thatTi-8Mo-8V-2Fe-3Al alloy has good ductility in the as-welded condition,and that by aging for a short period at 900 F. (2 hours) a simultaneousincrease in both strength and ductility can be brought about. Theapplication of a short post-Weld aging cycle to improve the propertiesof the alloy of this invention is a further important point. Table VIIshows that by prolonging the aging time at 900 F. to 4 hours, weldmentsmay attain a strength of over 180 K s.i., with good ductility. By agingat 1100 F. a condition of intermediate strength With ductility isproduced. By contrast, aging Ti-lSV-llCr-3Al alloy at 1100 F. followingwelding results in embrittlement. Hence, variation of aging temperaturein the range 900-1100 F. -is less important for Ti-8Mo-8V-2Fe-3Alweldments than Ti-13V-11cr-3Al weldments and the lack of a criticalpost-Welding aging temperature constitutes another aspect of thisinvention.

TABLE VIL-WELDED PROPERTIES F '1i-8M0-sv-21re-3A1 ALLOY (BUTT WELDS, NOFILLER, 0.060 SHEET HEAT TREATED 1,500 F.-10 MINUTES-AC) Elon- Testgation temper- UTS, YS, percent Modulus, Treatment ature K.s.1 K.s.i. inp.s.i. X(x

l Welded plus 900 F.-2 hours-AC. 2 Welded plus 900 F.-4 hours-AC. 3Welded plus 000 F.-8 hours-AC. 4 Welded plus 900 F.-16 hours-AC.

Another useful feature of the alloy of this invention is that aging at1100 F. for S hours or more results in the (a.) Tensile properties asabove stabilized Elongation percent in 2" Test UTS, YS, Mod- NTS, NTS/temperature K s.i. K s.i. L U T ulus K s.i. UTS

(b) Following creep exposure Creep exposure Subsequent tensileproperties Tern Elon- Modpera- Percent gation ulus ture, Stress, Time,defor- UTS, YS, percent p.s.i F. K s.i.l hours mation K .s 1 K s.i. in1" X10 60m-r" 93- 5 0.150 157 142 1e 15. o 500 0. 193 156 147 17 15. 1

12 See footnotes Table VI.

The mechanical properties of Ti-8Mo-8V-2Fe-3Al in the form of 1/z-inchplate are shown in the following Table IX. The alloy is readilyair-hardenable at this gage. Similar results were obtained in .2 plate.The excellent notch properties and plane strain crack propagationresistance are inherent features of this alloy.

TABLE IX.MECHANICAL PROPERTIES OF 1/2 THICK PLATE OF Ti8Mo- SV-ZFeBAlElon- RA gation Modulus UTS, YS, perpercent p.s.i. Heat-treatment K s.i.K s.i. cent in 1" X106 (a) Room temperature tensile test:

0 F.-1O minutes-AC 119 118 48 24 14. 1 116 114 53 27 12. 5 117 116 63 2912. 2 1,500

16 hours-AC 210 197 4 4 16. 2 Do 210 7 4 16. 0 Do 209 195 9. 5 8 16. 3(b) 600 F. s

1,500 F.10 minutes-AC plus 900 F.-

16 hours-AC 161 143 54 4 12. 6 Do 181 159 16 7 13. 2 179 157 16 4 13. 9

(c) RT notch tensile: Kt value NTS Average 1,500 1?.-10 minutes-AC plus900 F.

16 hours-AC 2. 8 262 D0..- 2. 8 263 263 D 2. 8 263 1,500 I". minu es-ACplus 900 F.-

8 hours-AC 8 233 D0". 8 223 226 D0 8 223 1,500 F. minu esAC plus 900 Fr-16 hours-AC 8 230 D0... 8 227 229 Do. 8 231 (d) 600 I". notel ensile:

1,500 F.10 minutes-AC plus 900 Fr- 16 hours-AC 2. 8 234 0... 2. 8 244241 Do 2. 8 246 1,500 F.-10 minutes-AC plus 900 F.

8 hours-AG 8 231 (e) Kia value 1,500

16 hours-AC Ti-8Mo-8V-2Fe-,3Alalso possesses good formingcharacteristics with `a minimum bend radius in the solution treatedcondition of 2T and 3T when stabilized. As shown in Table I, itpossesses good uniform elongation, and a low annealed yield strength,which would enable forming of larger parts to be done, or use of smallerpresses for equivalent parts.

In summary, it is claimed that the alloy of this invention,Ti-8Mo-V-2Fe-3Al, is superior to the present commercial alloyTil3V-llCr3Al in the following respects: Speed and control of aging,notch tensile strength, notched fatigue strength, stress corrosionresistance and weldability.

Alloys according to the invention may be produced by admixing titaniumsponge with the alloying ingredients in comminuted orm, compacting theadmixture into a consumable electrode and arc melting in a cold moldfurnace such as a water-cooled copper crucible to produce an ingot ofthe alloy. Homogeneity of the ingot may be improved by utilizing theingot as such as a consumable electrode and arc-remelting into a coldmold Crucible of larger diameter than the irst.

For breakdown operation the resulting ingot is heated to about 1860 F.and rolled or forged to a desired shape.

What is claimed is:

1. A titanium base alloy consisting essentially of about: 7 to 9% eachof molybdenum and vanadium, .1.5 to 2.75% iron, 2.5 to 3.5% aluminum, upto 0.2% in total amount of carbon, oxygen and nitrogen, balancetitanium, characterized in being substantially immune to stresscorrosion cracking, in being age hardenable to a yield strength of about180,000 p.s.i. on solution treating and thereafter aging at about 900 F.for about 8 hours, andlin having a tensile elongation of at least 5% inthe aged condition.

2. An alloy according to claim 1 containing about: 8% each of molybdenumand vanadium, 2% iron and 3% aluminum.

3. A wrought article made of an alloy according to claim 1.

4. A wrought and solution-treated article made of an alloy according toclaim 1 characterized by an 0.2% offset yield strength .of not more thanabout 120,000 p.s.i. and a tensile elongation of at least 10%.

5. An age-hardened titanium-base alloy according to claim 1characterized by an 0.2% offset yield strength of at least 180,000p.s.i. and a tensile elongation of at least 5% References Cited UNITEDSTATES PATENTS 2,754,203 7/ 1956 Vordahl 75-1755 2,918,367 12/1959Crossley et al. 75175.5 3,306,739 2/ 1967 Evans et al. 75-175.53,405,016 lO/1968 Jaiee et al 148--133 FOREIGN PATENTS 659,577 3/ 1963Canada.

776,440 6/ 1957 Great Britain.

782,564 9'/ 1957 Great Britain.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 14S-32.5, 133

